At Duke University, a school that likes to tout its cutting-edge research, a sex toy study being conducted by a behavioral economist and student health workers has roused criticism. For much of October, researchers recruited female Duke students to take part in a "sexually explicit" study on Tupperware-style parties in which sex toys, not kitchenware, are the draw.

For some, even serial monogamy seems too restrictive. The 1970s introduced the concept of "open marriage" in which couples stayed married but were free to date other people.More recently, polyamory -- the practice of having romantic relationships with multiple people at the same time with the full knowledge and consent of all involved -- has been getting a lot of attention.